The present invention relates to an improved method for testing components in a magnetic disk storage system, and more particularly relates to testing components in a system employing a thin film magnetic head.
As is well known, disk drives are an important part of most modern day computer systems. A disk drive typically employs one or more read/write magnetic heads whose performance is critical to the obtaining of satisfactory performance of the overall disk drive. It is thus of considerable importance, particularly for high volume head manufacturing, to provide for the rapid, accurate and reliable testing of the performance of a magnetic head. The provision of such testing is especially important in connection with the manufacture of new types of magnetic heads, such as thin film heads, which have different characteristics than conventional ferrite heads, and for which there is very little field experience.
An important characteristic indicative of the performance of a magnetic head is conventionally known as "bit shift" (also called peak shift) which is usually a result of the density of recording, the nature of the pattern being recorded, and also the presence of noise. As is well known, bit shift causes a bit to be detected at a time shifted by a certain amount from the expected time of detection, which if sufficiently large compared to the bit-cell time can cause data errors in a magnetic recording and reproducing system.
Another important characteristic indicative of the performance of a magnetic head is head timing asymmetry. The presence of head timing asymmetry is indicated, for example, when unwanted readback signal timing differences are produced dependent on the direction of change of the recorded magnetic transitions. Such head timing asymmetry can also be a source of unwanted bit shift.
Known approaches for measuring bit shift and head timing asymmetry have typically employed indirect techniques, such as by using reproduction frequency response measurements to determine "resolution", or by the use of isolated pulse superposition techniques. These known approaches have various disadvantages, such as being unduly time consuming, expensive and/or complex. In addition, the resolution approach can give quite inaccurate results when used for measuring the characteristics of thin film heads.